Continuous deposition of insulating material using multiple anodes alternated between positive and negative voltages

ABSTRACT

A method and an apparatus are disclosed for sputter deposition of an insulating material on a substrate in a continuous mode of operation. A novel design for an anode assembly and driving power supply is disclosed to permit this. Single or multiple anodes are used, which at any given time may be biased negatively with respect to the plasma, so that any insulating material which may have been deposited thereupon may be sputtered away so as to provide a clean positive anode to the system, and at least for some period of time is biased positively so that it acts as an anode. The removal of any insulating material which may have formed on the anode structure permits its continuing effective use in collecting electrons from the plasma when it is biased positively, and therefore its continuing effective use as an anode for the system, permitting continuous operation of the system.

BACKGROUND OF THE INVENTION

The present invention generally relates to reactive plasma sputterdeposition techniques for forming and depositing insulating films onsubstrates and, more particularly, is concerned with a system and methodfor sputter deposition of an insulating material on a substrate.

Sputtering is a process wherein a target, usually a metal, is placed inposition near a plasma (a cloud of ions and electrons in equal numbers),in a chamber in which most of the air has been withdrawn. Well-knownconventional means are used to create the plasma. A negative voltage isproduced on the target, or cathode, relative to a separate electrodecalled the anode by connecting the negative lead of a dc power supply tothe target. The negative voltage on the target attracts the ions fromthe plasma, which are accelerated toward the target. Upon arrival thecollision of the ions with the target physically knocks out targetatoms. These target atoms travel from the target to a substrate placednearby, which becomes coated with them. The expelled target atoms alsocoat every other surface in the system, as for the most part, they areneutral and there is no practical way to direct their path. When ionsare withdrawn from the plasma, there immediately exists an excess ofelectrons in the plasma. These excess electrons are attracted to thepositive lead of the dc power supply used to create the target voltage,which positive lead is connected to a separate electrode called theanode or alternatively to the chamber walls, either of which, incollecting the electrons, provide for plasma current flow and thereforemay be considered as plasma current providing elements.

As described, this is a very common process for deposition of thinlayers of metals. It is widely used in the processing of semiconductors,and in creating the reflecting layer on compact discs and CD-ROMS,active layers on hard discs for computer storage, and layers of metalsfor many other functional and decorative applications.

The process described above is called dc sputtering, and requires thatthe target (or cathode) be conducting, because the ions arriving at thetarget must be able to accept one or more electrons from the target tobecome neutral gas atoms again in order to prevent charging of thetarget surface, which would create a retarding potential which wouldstop the process very quickly. Insulators do not have free electronsavailable for this purpose, so that an insulating target material cannotbe used. On the other hand, one can deposit layers of insulatingmaterial from a metallic target, by forming the insulator chemicallythrough reaction with a reactive background gas. This is called reactivesputtering. For example, Al₂ O₃ and SiO₂ can be created from aluminumand silicon targets, respectively, if oxygen gas is present inappropriate quantities in the background gas filling the chamber.

There is increasing commercial interest in processes involvingdeposition of such insulating films. This interest comes about at leastin part because of the application of such processes to the depositionof wear resistant coatings; insulating films for microcircuits(including devices such as thin film heads) or electronic devices suchas capacitors; sophisticated architectural glass coatings; coatings onpolyester film for architectural glass laminates or oxygen barriers forfood packaging; heat reflecting coatings for high efficiency lamps orinduction furnace heat shields; deposition of barrier and functionallayers for flat panel displays, including the ITO glass used in LCDdisplays; and myriad other similar functional applications. Added tothis are the many reactive PVD processes used to create decorativeeffects on a wide variety of plastic, natural and artificial fiber, andmetal substrates.

A problem occurs in these cases, however, when the reaction product isan electrical insulator. Since, as described above, the insulating filmcoats every surface in the chamber (which it will eventually do) then itwill surely eventually coat the anode. As this happens the conductionpath for the electrons is coated over, and the process cannot besustained. This has been termed the "disappearing anode" problem. In thepast the reactive process was run until this effect began to createserious problems, whereupon the system was opened to mechanically scruboff the offending insulating layer from the anode to create a newmetallic surface. Thus continuous operation without this maintenance isnot possible.

Another drawback related to the coating of the anode with an insulatoris that this insulator will generally charge up as the electrons attemptto collect there. This charge can cause an electric field in theinsulating film on the anode which may exceed the dielectric strength ofthe film material. When this occurs an arc may be formed and the energyin this arc may cause portions of the film to be ejected from the anode,creating particulates which can become included in the film growing onthe substrate, causing defects which may be unacceptable in the finalproduct.

Este, et al, in an article entitled "A Quasi-direct-current SputteringTechnique for the Deposition of Dielectrics at Enhanced Rates",published in J. Vac. Sci. Technol. A, vol. 6, No. 3 (May/June 1988),proposed an approach to the sputtering process which uses two targetsalternately for deposition of dielectric or insulating films. The powersupply, which in this case has an alternating potential output, isconnected to the two targets so that they are driven alternativelypositive and negative with respect to one another. This causes each toact as an anode for the other. If the reversal takes place often enough,only a very thin layer of insulator will be formed on the target actingas an anode, and this very thin layer can be sputtered away when it isthat target's turn to be negative. This is possible because theinsulator does not stop the sputtering process at once, but due tocharging effects its presence will slow and eventually stop the process.If the layer is very thin it can be sputtered away before the processstops. The usual time for reversal is a few tens of microseconds, inorder that there be too little time for a thick layer to form. See alsothe paper by Schiller et al entitled "Pulsed Magnetron SputterTechnology", published in the Proceedings of the 1993 InternationalConference on Metallurgical Coatings and Thin Films, Surf. Coat. Tech.Vol. 61, (1993) page 331, which covers a dual magnetron target approachsimilar to that of Este et al in that each of the targets acts withinone cycle of the output of the power supply once as the cathode and onceas the anode.

For the most part this has proved to be a successful approach to theproblem of the "disappearing anode". It does have the disadvantage,however, of requiring two targets, which adds to the expense of thesystem and also complicates the maintenance. Also, it is difficult toretrofit this dual target process into existing sputtering systemsbecause there often is no room for the second target.

A more serious drawback to the dual target approach is caused by thefact that appropriate design of the target assembly usually involvesmagnets to create a magnetic field above the target surface to enhancethe plasma density. This magnetic field impedes the flow of electrons tothe target. Thus an appropriate design for a cathode is generally not agood design for an anode, which calls for unimpeded collection ofelectrons from the plasma. In a sputtering system there is a potentialdifference between the plasma and the target, or cathode, which iscalled the "cathode fall". Similarly there is a potential differencebetween the plasma and the anode, generally much smaller, which iscalled the "anode fall". In a well designed system almost all of thevoltage of the power supply appears as cathode fall and little appearsas anode fall. In a typical case the cathode fall might be 600 volts andthe anode fall less than 20 volts. With the dual target system, on theother hand, the anode fall is increased to much larger values, often aslarge as 50 to 100 volts. This creates two serious symptoms. First, thehigher anode fall changes the plasma potential such that a higher energysubstrate bombardment occurs. This can be beneficial, as some ionbombardment can help make the growing film more dense, but substratebombardment also equates with substrate heating, and this can be asignificant disadvantage if the substrate is composed of a heatsensitive material, such as plastic. Secondly, since the power supplycurrent passes through the anode, the product of the anode fall and thecurrent represents power loss in the anode. This in itself may be aproblem, but even if the anode can withstand the heating effect, thepower loss in the anode must necessarily subtract from the power of thepower supply (that is the actual device or even any part of thecircuitry involved in or which acts to facilitate some supply of powerto the element involved) and thus reduce the power available to thecathode for sputtering purposes. Thus the deposition rate equivalent toeach watt delivered by the power supply is reduced by the proportion ofthe anode fall to the cathode fall. In the example case above for dualcathode sputtering, the anode would receive 1/6 of the power (thecurrent times 100 volts out of the 600 volts available from the powersupply) and the cathode the balance of 5/6. This represents a loss of16.7% of the potential sputtering power, while an anode fall of 10 voltswould "steal" but 1.7% of the potential power to heat the anode. Ofcourse, other losses may also exist, but a substantial anode fall canmaterially lower the deposition rate.

Consequently, a need exists for a different approach to overcome theabove-described drawbacks of the prior art reactive sputteringprocesses. The present invention permits single target operation with aseparate anode assembly with a small anode fall and therefore lowsubstrate bombardment and good utilization of the sputtering power,without suffering from the problem of the "disappearing anode".

SUMMARY OF THE INVENTION

It is an object of the present invention, therefore, to provide an anodefunction for reactive sputtering systems with characteristics whichcreate a relatively small anode fall relative to that observed in dualcathode sputtering systems.

It is a further object of this invention to reduce substrate heating insputtering systems below that normally observed in dual cathodesputtering systems.

It is yet another object of the present invention to increase thesputtering rate of the target in a sputtering system for each wattdelivered by the cathode power supply above that normally observed indual cathode sputtering systems.

It is another object of the present invention to provide continuousoperation by preventing stoppage of the reactive sputtering process dueto buildup of an insulating film on the anode(s) of the system.

It is yet a further object of this invention to improve uniformity ofdeposition by avoiding the nonuniform electric fields caused by thebuildup of insulating films on the anode(s) of the system.

It is yet a further goal of the invention to prevent arcing that mayoccur due to the buildup of insulating films on the anode(s) of thesystem, and thereby prevent the particulate matter dispersed in thechamber caused by the mechanical forces created by such arcing.

Accordingly, the present invention is directed to a system for sputterdeposition of an insulating material on a substrate in a continuous modeof operation. The present invention discloses a novel design for ananode assembly to permit this, which assembly comprises a plurality ofanodes, at least one of which at any given time might be biasedpositively (that is, the opposite polarity of the target) so as toprovide a clean positive anode to the system, or more generally in an"electron-collecting state", and at least for some period of time mightbe biased negatively with respect to the plasma (that is, in the samepolarity as the target), or more generally in an "ion-collecting state"so that any insulating material which may have been deposited thereuponmay be sputtered away. This removal of any insulating material which mayhave formed on the anode structure permits its continuing effective usein collecting electrons from the plasma when it is biased positively,and therefore its continuing effective use as an anode for the system.This permits continuous operation of the system. A cathode power supply(as mentioned earlier, that is, that is the actual device or even anypart of the circuitry involved in or which acts to facilitate somesupply of power to the cathode) can be used to create a negative (ioncollecting) potential on the cathode; this supply may be separate fromthe anode power supply, and may cause the state of the anodes to bealternated between the ion- and electron-collecting states.

The present invention is also directed to a method for sputterdeposition of a target to create an insulating material on a substratein a continuous operating mode. The method comprises the acts ofproviding a coating chamber, generating a plasma, providing a targetcathode to be sputtered and at least two anodes, maintaining the cathodeat a negative potential, but either switching or alternating the anodesbetween an ion-collecting (sputtering) state and an electron-collectingstate. The existence of the ion-collecting state in this method permitssputtering of any insulating deposition on the anodes and thus permits acontinuous mode of operation.

To strictly avoid contamination of the growing film on the substrate,the anode may preferably be made of the same material as the target,since some of its material may be deposited on the substrate as well. Onthe other hand, as already pointed out, very little of the anode isactually sputtered, and if a shield is arranged to intercept themajority of the sputtered material from the anode so that it does notarrive at either the target or the substrate, contamination can be keptto a minimum, and other materials may be used.

Such an approach is easier to retrofit into existing systems because theanode is physically much smaller than an additional target, andgenerally there exists sufficient room in a system to place therequisite pair of anodes.

In one embodiment, the present invention uses two anodes, together witha single target, to permit continuous operation. A small auxiliary acpower supply (called the "anode supply"), connected between the twoanodes, produces an ac voltage of the order of several hundred voltspeak. When one anode is positive, and is therefore acting as an anode,the other is made negative with respect to the plasma. This negativevoltage of the anode surface. The other anode, meanwhile, is drivenpositive during this period, and this element therefore attracts andcollects the electrons from the plasma (the "electron-collecting"state). On alternate half cycles of the anode supply, each anodealternately acts either as an electron collector, or as anion-collector; in the latter state the anode is sputtered. Thesputtering process keeps the anode free of insulating film. Since verylittle sputtering power is required to remove the thin film formed oneach half cycle, very little of the anode material is actually sputteredaway, and the anode can be made to last a long time.

In another embodiment, a plurality of anodes are placed in the chamberand each is driven negative to be sputtered during some portion of analternation cycle. At any time at least one of the anodes is maintainedat a positive potential to attract and collect electrons from theplasma. Alternatively, all of the anodes may be driven negative at onceduring the cycle preferably so that the period during which all of theanodes are negative is not long enough to extinguish the plasma, bywhich we mean that the density of the ions and electrons in the plasmahas been reduced to levels below 10% of the steady state value.

It should be noted that, while the conception of the present inventionwas inspired by the need for a clean anode in reactive sputtering ofinsulating materials, it is not uncommon that anodes in metallicdeposition can become coated with poorly conducting films back scatteredonto them by the background gas, and therefore the present invention hasapplication beyond reactive sputtering of insulators.

It is possible as well to use a single anode which is pulsed to anegative voltage on a regular basis. In this case there may be, for theperiod of the negative pulse, no specific anode in the system. Theelectrical circuit may then be arranged so that for this period thechamber walls become an anode or the current providing element, althoughin some cases it may be possible for the plasma to provide a smallquantity of ions without an anode in the system, and in these cases noconnection to the chamber wall is necessary. A version of this generalapproach may be taken with multiple elements by eliminating one of theconditions outlined previously; that is, all of the elements could betaken negative simultaneously for some period. Regardless of the numberof elements, the time for which any element is kept negative shouldlikely be long enough to attract ions from the plasma to the element andto sputter away the material deposited there.

In any of these embodiments, it is necessary for the cathode to be heldnegative with respect to the plasma so that it may be sputtered and afilm be deposited. This is accomplished with a cathode power supply,which may be a simple dc supply or may be a high frequency supply. Inthe latter case a so-called "self bias" potential appears on the targetsurface due to the asymmetric nature of the plasma over a range offrequencies defined by a lower limit whereat the ions can fully reachthe cathode in a single half cycle, and an upper limit whereat theelectrons cannot reach the cathode in a single half cycle of thealternating waveform. Between these two limits, the electrons cantraverse the gap between the plasma and the cathode surface, while theions cannot, and the asymmetry thus created cause a self-bias to appearon the cathode in a manner well known to those skilled in the art ofplasma processing.

BRIEF DESCRIPTIONS OF THE DRAWINGS.

FIG. 1 shows a conventional single target sputtering system using dcpower.

FIG. 2 shows a conventional dual target sputtering system using acpower.

FIG. 3 shows one embodiment of the present invention with two anodesdriven by a sinusoidal voltage source with the voltage on the two anodes180° out of phase from one another.

FIG. 4 shows another embodiment of the present invention with threeanodes driven by a three-phase sinusoidal source with the voltage on theanodes 120° out of phase, each from the another.

FIG. 5 shows a multi phase multiple anode configuration wherein aplurality of anodes are driven by a pulsed power supply with a pulsesequencer controlling the pulse voltages on each anode.

FIG. 6 shows an embodiment wherein a single anode is disposed in achamber with an auxiliary electrical element which may be a diode or acapacitor.

FIG. 7 shows a single anode configuration of the present inventionwherein the electrical element of FIG. 6 is replaced with a shortcircuit. Also shown is a detail of the deposited film on the walls andhow it forms an equivalent capacitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As can be easily understood, the basic concepts of the present inventionmay be embodied in a variety of ways. It involves both processes ormethods as well as devices to accomplish such. In addition, while somespecific circuitry is disclosed, it should be understood that these notonly accomplish certain methods but also can be varied in a number ofways. Importantly, as to all of the foregoing, all of these facetsshould be understood to be encompassed by this disclosure.

FIG. 1 shows a conventional single target system. In this case there mayexist a discrete anode 5 or an alternative connection may be madewhereby the positive lead of sputtering power supply 6 is connected tothe chamber 1 rather than to anode 5. In this case anode 5 may bedispensed with. The alternative connection is shown in dotted lines inFIG. 1. Ions are attracted to target 4 from plasma 2 and upon strikingtarget 4 cause sputtered atoms to be ejected from target 4 in accordancewith well-known principles. These sputtered atoms traverse the spacebetween the target and the substrate 3 and deposit there, creating athin film of the target material thereupon.

Should the target be metallic and the background (sputtering) gas be aninert gas such as Argon, depositing metal films on substrate 3, thereare little problems with a system configured such as in FIG. 1. If,however, a reactive gas is introduced into chamber 1 in order to createa chemical compound on the target, and if the reaction product is anelectrical insulator, a problem surfaces. Since the insulating film willcoat every surface in the chamber 1, it will eventually coat the anode(or in the case of the alternative connection, the chamber walls). Asthis happens the conduction path for the electrons streaming from theplasma 2 is coated over, and the process cannot be sustained. This iswhat has been termed the "disappearing anode" problem. While it ispossible to open chamber 1 and mechanically scrub off the offendinginsulating layer from the anode or the chamber walls to create a newmetallic surface, this is costly and time consuming and it would bedesirable to avoid having to do so. This desire is believed to haveinspired the invention of the system shown in FIG. 2. In FIG. 2 twotargets 7 and 8 are disposed in the space normally occupied by thesingle target 4 in FIG. 1 and no separate anode is provided. A source ofalternating power 10 is applied between the two targets 7 and 8 throughisolating transformer 9. In this way each target 7 can act as an anodefor target 8 when the voltage between the targets is such that target 7is positive with respect to target 8. Similarly, target 8 can act as ananode for target 7 when the voltage between the targets is such thattarget 8 is positive with respect to target 7. Because the power supply10 is an alternating source of power, this situation is reversed everyhalf cycle of the current. If the reversal takes place often enough,only a very thin layer of insulator will be formed on target 7 when itis acting as an anode, and this very thin layer can be sputtered awaywhen it is the turn of target 7 to be negative. The same may be said fortarget 8. Normally in systems such as shown in FIG. 2 the frequency ofthe power supply 10 is about 40 kHz, corresponding to a reversal every12.5 μs.

As mentioned previously, this has proved to be a successful approach buthas the disadvantage of requiring two targets 7 and 8, adding to theexpense of the system and complicating maintenance. In addition,appropriate design for a target assembly such as target 7 or 8 mayinvolve creation of a magnetic field above the target surface, and thisfield can impede the flow of electrons to the target. This may increasethe anode fall (the voltage between the positive target and plasma 2) tovalues as large as 100 volts, in turn creating higher energy substratebombardment and substrate heating. Also, the specific deposition rate(rate per watt) can be reduced by the proportion the anode fall is tothe cathode fall (the voltage between the negative target and plasma 2).

One of the preferred embodiments of the present invention is shown inFIG. 3. In chamber 1 are disposed substrate 3, target 4, and at leasttwo anodes 11 and 12. Anode drive supply 14 provides an alternatingvoltage isolated by anode transformer 13 to the two anodes such thatwhen anode 11 is driven positive, anode 12 is driven negative and viceversa. The secondary of transformer 13 has a "tap", by which we meanthat a connection is made to the secondary winding at a point removedfrom the ends. The tap may or may not be in the electrical center of thetransformer so as to effect an equal division of the voltage. Target 4is held negative with respect to the tap of the secondary of transformer13 by cathode power supply 6, which supplies the sputtering power.

When the voltage cycle of the anode supply 14 is such that anode 11 ispositive with respect to anode 12, anode 11 will collect electrons fromthe plasma (i.e., it can be said to be in an "electron-collecting"state). This will cause electron current in the left half of thesecondary of transformer 13, flowing from anode 11 to the positive leadof de supply 6. These electrons combine with ions arriving at target 4from plasma 2 to complete the circuit. Meanwhile, anode 12 is drivennegative with respect to the plasma by the action of transformer 13 andanode supply 14, and this negative potential attracts additional ionsfrom the plasma (i.e., the anode is in an "ion-collecting" state). Theseions cause sputtering of the surface of anode 12. This sputtering ofanode 12 removes any buildup of insulating materials which might haveformed there on the previous half cycle of the ac power supply 14 whenanode 12 was positive and therefore near to the plasma potential.

Similarly, when the voltage cycle of the anode supply 14 is such thatanode 12 is positive with respect to anode 11, anode 12 will collectelectrons from the plasma. This will cause electron current in the righthalf of the secondary of transformer 13, flowing from anode 12 to thepositive lead of de supply 6. These electrons combine with ions arrivingat target 4 from plasma 2 to complete the circuit. Meanwhile, anode 11is driven negative with respect to the plasma by the action oftransformer 13 and anode supply 14, and this negative potential attractsions from the plasma which causes sputtering of the surface of anode 11.This sputtering of anode 11 removes any buildup of insulating materialswhich might have formed there on the previous half cycle of the ac powersupply 14 when anode 11 was positive and therefore near to the plasmapotential.

Thus each of the anode elements 11 and 12 act alternatively as trueanodes (electron collectors) and as sputtered cathodes (ion collectors)depending upon the instantaneous polarity of the ac power supply 14.

Another embodiment of the present invention is shown in FIG. 4. In thisfigure an additional anode 15 has been placed near target 4 as comparedto FIG. 3. The three anodes 11, 12, and 15 are driven by a three phasepower supply 17 through a three phase transformer 16, here shown in adelta-wye connection. Of course, transformer 16 may also be configuredin a wye-wye connection as is well known in the art. It is a feature ofthe wye connection that one lead of each of the three secondary windingsis connected to a common point, usually called the "neutral" point. Thecathode power supply 6 is connected with its positive lead to thiscommon point and its negative lead to the cathode itself.

FIG. 5 shows yet another embodiment of the present invention. In thiscase a multiplicity of anodes 18 are placed in proximity to the target 4and are driven by pulsed anode power supply 19. There may always be atleast one anode at a positive potential in order that it may be near tothe plasma potential and therefore be able to collect electrons, or atleast that any period during which all anodes are negative with respectto the plasma is kept short enough that the plasma is not extinguished.(As intended here, and as one of ordinary skill in the art would readilyunderstand, at least one anode would still "always" be in anion-collecting state--even if there were brief interruptions--so long asthe plasma were not extinguished.) This might ensure that the plasmapotential will remain steady with respect to the chamber and that thesputtering process continues. The pulses on the anodes may be placedthere in some sequence by pulse sequencer unit 20. The pulses might beso arranged that over one cycle of the sequence created by pulsesequencer unit 20, each anode might have assumed a negative potentialrelative to the plasma, in order that it attract ions and therefore besputtered. This action should cause removal of a thin film of materialfrom each anode on each cycle of pulse sequencer unit 20, which mightensure that its metallic surface remains conducting so that it may be anefficient attractor for electrons (i.e., act efficiently as an anode)when it is, in its turn, driven positive by pulsed power supply 19. Ofcourse, the time any anode spends in a negative and positive conditionneed not be the same, and the time spent in either condition may bedifferent for each anode, and these timings may be altered to optimizethe process, taking into consideration the relative mobility of the ionsand electrons, among other factors. As those skilled in the art wouldreadily understand, such pulsing might also offer an advantage of moreevenly powering the plasma, for instance as compared to a sinusoidallyalternating type of system.

FIG. 6 shows a single anode embodiment of the present invention. Thisdiffers from FIG. 1 in the addition of a series electrical element 21connecting the positive lead of the cathode supply 6 to the chamber 1.This element 21 is shown as a diode, but it may also be a capacitor.Anode power supply 14 is connected in series with the anode 5 viaisolation transformer 13. When the polarity of the anode power supply 14is such that the anode is driven positive, the positive lead of thecathode supply 6 is driven negative and the cathode current flowsthrough the secondary winding of transformer 13 to anode 14. When thepolarity of the anode power supply 14 is such that the anode is drivennegative, the positive lead of the cathode supply 6 is driven positiveand the diode conducts, making the chamber a temporary anode.

If the electrical element 21 shown as a diode is replaced by acapacitor, then the capacitor will charge to an average value which willbe dependent upon the timing of the anode supply 14. The capacitor 21will be charged by the sputtering current of both the sputtering ofanode 5 and target 4 during the period when the anode 5 is drivennegative, and will be discharged when the anode 5 is driven positive.

It may be noted that once the chamber has been coated by an insulatinglayer, that thin film forms a capacitor with the plasma, and will act inthe same way as the capacitor 21. This may be seen in FIG. 7. Here asingle anode system is shown with an expanded view of the chamber wall,showing the chamber wall 22 coated with the insulating film 23 formingan equivalent capacitor 24. This equivalent capacitor would haveeffectively been in series with electrical element 21 were it placed inthe circuit, making this electrical element redundant. Therefore in FIG.7 the electrical element has been replaced with a direct connection 25.The equivalent capacitor then takes the place of the capacitiveelectrical element 21. In this case the chamber acts as an anode untilit becomes coated. At that point the anode element takes over, as it hasbeen kept clean by sputtering action due to the periodic negativepotential placed upon it relative to the plasma by the action of anodedrive supply 14. Care must be taken in either case to design thetransformer 13 so that it may handle dc current in its secondary windingwithout saturation, as the current in the secondary will not, in thegeneral case, average to zero. Care must be taken in either case todesign the transformer 13 so that it may handle dc current in itssecondary winding without saturation, as the current in the secondarywill not, in the general case, average to zero.

In all embodiments, should it be desired that a chemical compound beformed at the substrate, a reactive gas flow may be introduced into thechamber so that the sputtered material from the target may react withthe gas to form a compound on the substrate. Common examples may besputtering silicon in the presence of oxygen to obtain SiO₂ ; sputteringaluminum in the presence of oxygen to obtain Al₂ O₃ ; sputteringaluminum in the presence of nitrogen to obtain AlN, etc.

As mentioned earlier, this invention can be embodied in a variety ofways. In addition, each of the various elements of the invention andclaims may also be achieved in a variety of manners. This disclosureshould be understood to encompass each such variation, be it a variationof an embodiment of any apparatus embodiment, a method or processembodiment, or even merely a variation of any element of these.Particularly, it should be understood that as the disclosure relates toelements of the invention, the words for each element may be expressedby equivalent apparatus terms or method terms--if only the function orresult is the same. Such equivalent, broader, or even more generic termsshould be considered to be encompassed in the description of eachelement or action. Such terms can be substituted where desired to makeexplicit the implicitly broad coverage to which this invention isentitled. As but one example, it should be understood that all actionmay be expressed as a means for taking that action or as an elementwhich causes that action. Similarly, each physical element disclosedshould be understood to encompass a disclosure of the action which thatphysical element facilitates. Regarding this last aspect, the disclosureof a "switch" should be understood to encompass disclosure of the act of"switching"--whether explicitly discussed or not--and, conversely, werethere only disclosure of the act of "switching", such a disclosureshould be understood to encompass disclosure of a "switch." Such changesand alternative terms are to be understood to be explicitly included inthe description.

The foregoing discussion and the claims which follow describe thepreferred embodiments of the invention. Particularly with respect to theclaims, it should be understood that changes may be made withoutdeparting from their essence. In this regard it is intended that suchchanges would still fall within the scope of the present invention. Itis simply not practical to describe and claim all possible revisionswhich may be accomplished to the present invention. To the extent suchrevisions utilize the essence of the invention each would naturally fallwithin the breadth of protection accomplished by this patent. This isparticularly true for the present invention since its basic concepts andunderstandings are fundamental in nature and can be applied in a varietyof ways to a variety of fields.

Furthermore, any references mentioned in the application for this patentas well as all references listed in any information disclosureoriginally filed with the application are hereby incorporated byreference in their entirety to the extent such may be deemed essentialto support the enablement of the invention(s). However, to the extentstatements might be considered inconsistent with the patenting ofthis/these invention(s) such statements are expressly not to beconsidered as made by the applicant(s).

We claim:
 1. A system for sputter deposition of a cathode material toform a material upon a substrate in a continuous operating mode, saidsystem comprising:(a) a coating chamber in which a plasma is createdcomprising ions and electrons; (b) at least two anodes disposed in saidchamber; (c) a cathode disposed in said chamber adjacent to said plasma,said cathode containing atoms that can be sputtered therefrom inresponse to bombardment by said ions from said plasma to deposit a filmon a surface of said substrate; (d) a cathode power supply connected tosaid cathode which maintains said cathode at a negative potentialrelative to said plasma; (e) an anode power supply connected to saidanodes so as to drive said anodes alternately to an ion-collecting statewherein said anodes attract said ions when maintained at a negativepotential relative to said plasma, and an electron-collecting statewherein said anodes attract said electrons when maintained at a positivepotential relative to said plasma, said ion-collecting state and saidelectron-collecting state occurring while said cathode is maintained ata negative potential relative to said plasma.
 2. The system of claim 1wherein said cathode power supply comprises a dc power supply.
 3. Thesystem of claim 1 wherein said cathode power supply comprises an acpower supply at a frequency such that said cathode assumes a self biaspotential which is negative relative to the plasma.
 4. The system ofclaim 1 wherein said anode power supply has a cycle, and wherein duringsaid cycle at least one of said anodes is always in saidelectron-collecting state.
 5. The system of claim 1 wherein said anodepower supply has a cycle, and wherein during said cycle the periodduring which every one of said anodes is in said ion-collecting state isless than the time required to extinguish said plasma.
 6. The system ofclaim 1 wherein said anode power supply comprises:a) an ac supply; andb) a transformer having at least one primary winding connected to saidac supply and at least one secondary winding connected to saidanodes,wherein said secondary windings connect to a common point, andwherein said cathode power supply comprises a dc power supply having anegative lead connected to said cathode and a positive lead connected tosaid common point.
 7. The system of claim 1 wherein said anode powersupply comprises:a) an ac supply; and b) a transformer having at leastone primary winding connected to said ac supply and at least onesecondary winding connected to said anodes,wherein are disposed twoanodes and wherein said transformer has a single secondary winding witha tap, and wherein said cathode power supply comprises a dc power supplyhaving a negative lead connected to said cathode and a positive leadconnected to said tap.
 8. The system of claims 4 or 5 wherein said anodepower supply comprises a pulsed power supply and wherein said pulsedpower supply causes each anode to be switched between saidion-collecting state and said electron-collecting state.
 9. The systemof claim 1 wherein said coating chamber contains a reactive gas.
 10. Thesystem of claim 9 wherein said atoms sputtered from said cathode inresponse to bombardment by said ions react with said reactive gas toform and deposit said film.
 11. A system for sputter deposition of acathode material to form a material upon a substrate in a continuousoperating mode, said system comprising:(a) a coating chamber in which aplasma is created comprising ions and electrons; (b) at least one anodedisposed in said chamber; (c) a cathode disposed in said chamberadjacent to said plasma, said cathode containing atoms that can besputtered therefrom in response to bombardment by said ions from saidplasma to deposit a film on a surface of said substrate; (d) a cathodepower supply connected to said cathode which maintains said cathode at anegative potential relative to said plasma; (e) an anode power supplyconnected to said anode so as to cause said anode to be drivenalternately to an ion-collecting state wherein said anode attracts saidions when said anode is maintained at a negative potential relative tosaid plasma, and an electron-collecting state wherein said anodeattracts said electrons when said anode is maintained at a positivepotential relative to said plasma, said ion-collecting state and saidelectron-collecting state occurring while said cathode is maintained ata negative potential relative to said plasma.
 12. The system of claim 11wherein said cathode power supply comprises a dc power supply.
 13. Thesystem of claim 11 wherein said cathode power supply comprises an acpower supply at a frequency such that said cathode assumes a self biaspotential which is negative relative to the plasma.
 14. The system ofclaim 11 wherein said anode power supply has a cycle, and wherein duringsaid cycle the period during which said anode is in said ion-collectingstate is less than the time required to extinguish said plasma.
 15. Thesystem of claim 11 wherein said cathode power supply is connected tosaid chamber through a series electrical element which provides forplasma current flow during the period said anode is caused to be in saidion-collecting state by said anode power supply.
 16. The system of claim15 wherein said series electrical element comprises a diode.
 17. Thesystem of claim 15 wherein said series electrical element comprises acapacitor.
 18. The system of claim 15 wherein said series electricalelement is replaced by a short circuit.
 19. The system of claim 11wherein said coating chamber contains a reactive gas.
 20. The system ofclaim 19 wherein said atoms sputtered from said cathode in response tobombardment by said ions react with said reactive gas to form anddeposit said film.
 21. A method for sputter deposition of an insulatingmaterial on a substrate in a continuous operating mode, said methodcomprising:a) providing a coating chamber in which a plasma is createdof ions and electrons; b) providing at least two anodes in said chamber;c) providing a cathode in said chamber adjacent to said plasma, saidcathode containing atoms that may be sputtered therefrom in response tobombardment by ions from said plasma to form and deposit a material onsaid substrate; d) maintaining said cathode at a negative potentialrelative to said plasma; and e) alternating said anodes between anion-collecting state wherein said anodes attract said ions whenmaintained at a negative potential relative to said plasma, and anelectron-collecting state wherein said anodes attract said electronswhen maintained at a positive potential relative to said plasma, saidion-collecting state and said electron-collecting state occurring whilesaid cathode is maintained at a negative potential relative to saidplasma.
 22. The method of claim 21 wherein said act of maintaining saidcathode at a negative potential relative to said plasma comprisesconnecting a dc power supply to said cathode.
 23. The method of claim 21wherein said act of maintaining said cathode at a negative potentialrelative to said plasma comprises supplying to said cathode an acvoltage at a frequency such that said cathode assumes a self biaspotential which is negative relative to the plasma.
 24. The method ofclaim 21 wherein said act of alternating said anodes comprisesalternating said anodes in a cycle, and wherein during said cycle atleast one of said anodes is always in said electron-collecting state.25. The method of claim 21 wherein said act of alternating said anodescomprises alternating said anodes in a cycle, and wherein during saidcycle the period during which every one of said anodes is in anion-collecting state is less than the time required to extinguish saidplasma.
 26. The method of claims 24 or 25 wherein said act ofalternating said anodes in a cycle further comprises holding each ofsaid anodes in an ion-collecting state for at least a portion of saidcycle.
 27. The method of claim 21 wherein said act of alternating saidanodes comprises providing a voltage from an ac supply through atransformer having at least one primary winding connected to said acsupply and at least one secondary winding connected to said anodes. 28.The method of claim 27 wherein said secondary windings of saidtransformer connect to a common point, and wherein said act ofmaintaining said cathode at a negative potential relative to said plasmacomprises:a) connecting the positive lead of a dc power supply to saidcommon point; and b) connecting the negative lead of said dc powersupply to said cathode.
 29. The method of claim 27 wherein two anodesare provided and wherein said transformer has a single secondary windinghaving a tap, and wherein said act of maintaining said cathode at anegative potential relative to said plasma comprises:a) connecting thepositive lead of a dc power supply to said tap; and b) connecting thenegative lead of said dc power supply to said cathode.
 30. The method ofclaim 21 further comprising providing a reactive gas to said chamber.31. The method of claim 30 further comprising choosing said reactive gassuch that said atoms sputtered from said cathode in response tobombardment by said ions react with said reactive gas to form anddeposit a material which is insulating.
 32. A method for sputterdeposition of a material on a substrate in a continuous operating mode,said method comprising:a) providing a coating chamber; b) generating aplasma of ions and electrons therein; c) providing at least one anode insaid chamber; d) providing a cathode in said chamber adjacent to saidplasma, said cathode containing atoms that are sputtered therefrom inresponse to bombardment by ions from said plasma to form and deposit amaterial on said substrate; e) maintaining said cathode at a negativepotential relative to said plasma, and; f) alternating said anode so asto cause said anode to be driven alternately to an ion collecting statewherein said anode attracts said ions when said anode is maintained at anegative potential relative to said plasma, and an electron-collectingstate wherein said anode attracts said electrons when said anode ismaintained at a positive potential relative to said plasma, saidion-collecting state and said electron-collecting state occurring whilesaid cathode is maintained at a negative potential relative to saidplasma.
 33. The method of claim 32 wherein said act of maintaining saidcathode at a negative potential relative to said plasma comprisesconnecting a dc power supply to said cathode.
 34. The method of claim 32wherein said act of maintaining said cathode at a negative potentialrelative to said plasma comprises supplying to said cathode an acvoltage at a frequency such that said cathode assumes a self biaspotential which is negative relative to the plasma.
 35. The method ofclaim 32 wherein said act of alternating said anode comprisesalternating said anode in a cycle, and wherein during said cycle theperiod during which said anode is in said ion-collecting state is lessthan the time required to extinguish said plasma.
 36. The method ofclaim 34 or 35 wherein said act of maintaining said cathode at anegative potential relative to said plasma further comprises providingfor plasma current flow during the period said anode is caused to be insaid ion-collecting state.
 37. The method of claim 36 wherein said actof providing for plasma current flow during the period said anode iscaused to be in said ion-collecting state comprises utilizing a diode.38. The method of claim 36 wherein said act of providing for plasmacurrent flow during the period said anode is caused to be in saidion-collecting state comprises utilizing a capacitor.
 39. The method ofclaim 36 wherein said act of providing for plasma current flow duringthe period said anode is caused to be in said ion-collecting statecomprises utilizing a short circuit.
 40. The method of claim 32 furthercomprising providing a reactive gas to said chamber.
 41. The method ofclaim 40 further comprising choosing said reactive gas such that saidatoms sputtered from said cathode in response to bombardment by saidions react with said reactive gas to form and deposit a material whichis insulating.